Light Chain 1 of Microtubule-associated Protein 1B Can Negatively Regulate the Action of Pes1

Abstract

Pes1 was first identified as the locus affected in the zebrafish mutant pescadillo, which exhibits severe defects in gut and liver development. It has since been demonstrated that loss of Pes1 expression in mammals and yeast affects ribosome biogenesis, resulting in a block in cell proliferation. Pes1 contains a BRCA1 C-terminal domain, a structural motif that has been shown to facilitate protein-protein interactions, suggesting that Pes1 has binding partners. We used a yeast two-hybrid screen to identify putative interacting proteins. We found that light chain 1 of the microtubule-associated protein 1B (Mtap1b-LC1) could partner with Pes1, and deletion analyses revealed a specific interaction of Mtap1b-LC1 with the Pes1 BRCA1 C-terminal domain. We confirmed the integrity of the interaction between Pes1 and Mtap1b-LC1 by co-immunoprecipitation experiments. Protein localization studies in NIH3T3 cells revealed that exogenously expressed Pes1 was typically restricted to nuclei and nucleoli. However, exogenous Pes1 was found predominantly in the cytoplasm in cells that were forced to express Mtap1b-LC1. We also observed that the expression of endogenous Pes1 protein was significantly reduced or undetectable in nuclei when Mtap1b-LC1 was overexpressed, implying that a dynamic interaction exists between the two proteins and that Mtap1b-LC1 has the potential to negatively impact Pes1 function. Finally, we demonstrated that, as is the case when Pes1 expression is depleted by shRNA, overexpression of Mtap1b-LC1 resulted in diminished proliferation of NIH3T3 cells, suggesting that Mtap1b-LC1 has the potential to repress cell proliferation by modulating the nucleolar levels of Pes1.Ribosome biogenesis is a strictly regulated process that when disrupted has been shown to correlate with cancer and other human diseases (1). The mechanisms underlying ribosomal RNA (rRNA) processing and the assembly of pre-ribosomal subunits have been thoroughly described in both yeast and mammals (2). A combination of genetic and biochemical experiments has demonstrated that Pes1 is required for ribosome biogenesis in both cases (3, 4). Although originally identified as a mutant that affects embryonic development in the zebrafish, Pes1 is an evolutionarily conserved protein and is indispensable for viability of yeast and mice (3,(5)(6)(7)(8)(9). The analysis of Pes1 Ϫ/Ϫ mouse embryos revealed an essential requirement for Pes1 during pre-implantation stages of development because blastomeres lacking Pes1 failed to proliferate and exhibited a dramatic reduction in the abundance of ribosomes (3). In addition, recent studies have implicated Pes1 during transcriptional control of gene expression and in cell immortalization (10, 11). Pes1 contains a BRCA1 C-terminal (BRCT) 3 domain that is necessary for normal Pes1 function (7,8). BRCT domains have been identified in a wide variety of proteins, and it has been proposed that this domain mediates protein-protein interactions (12, 13). The presence of a BRCT domain, therefore, suggests that Pes1 inter...

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“…38 Previous studies have demonstrated that MAP1B-LC1 interacts with Pes1 and p53 to modulate cell proliferation and apoptosis. 39,40 Thus, loss of function of this gene may contribute to the cancer cell’s ability evade death signals and proliferate. Together, silencing of CCDC37 and MAP1B during development of COPD may contribute to the development of malignant NSCLC.…”

Microtubule‐associated Protein 1B Light Chain (MAP1B‐LC1) negatively regulates the activity of tumor suppressor p53 in neuroblastoma cells

“…Previous studies have demonstrated that MAP1B not only forms cross‐links between individual microtubules for stabilizing microtubule structure but can also interact with non‐microtubule‐associated proteins that can regulate microtubule stability [2]. It has been also reported that MAP1B has other novel functions [17]. One novel function of MAP1B‐LC1 is that it interacts with Pes1 and induces a cytoplasmic sequestration of nucleolar Pes1, which results in a reduction of cell proliferation.…”

“…MAP1B directly binds with glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH), essential in the local energy provision of cytoskeletal structures, and helps to keep this enzyme in close proximity to the cytoskeleton [16]. Recently, MAP1B‐LC1 has also been identified as an interacting partner of Pes1, which is required for ribosome biogenesis and cell proliferation [17]. The interaction with MAP1B‐LC1 induces a cytoplasmic sequestration of nucleolar Pes1, which results in a reduction of cell proliferation.…”